Diesel fuel composition and a method to improve filterability of diesel fuel

ABSTRACT

Disclosed is a stabilized diesel fuel composition comprising a) a diesel fuel with a cetane number less than or equal to 50, b) an effective amount of at least one compound selected from the group consisting of the cetane improvers and c) i) an effective stabilizing amount of at least one compound selected from the group consisting of the stable nitroxide compounds or ii) an effective synergistic stabilizing amount of at least one compound selected from the group consisting of the stable nitroxide compounds and at least one antioxidant compound selected from the group consisting of the aromatic amine antioxidants and the hindered phenolic antioxidants. The cetane improvers are for example nitrate esters. The diesel fuel compositions exhibit improved filterability.

This application is a continuation of U.S. application Ser. No.10/809,882, filed Mar. 25, 2004, pending, which claims the benefit under35 USC 119(e) of U.S. provisional application No. 60/459,020, filed Mar.31, 2003, which applications are incorporated by reference.

The present invention is aimed at stabilized diesel fuel compositionsthat comprise certain cetane improvers. The stabilized diesel fuelcompositions exhibit improved filterability. The diesel fuelcompositions comprise stabilizers selected from the group consisting ofthe stable nitroxide compounds and optionally the aromatic amine andhindered phenolic antioxidants. The cetane improvers are for examplenitrate esters.

The present compositions form reduced insoluble material that may clogfuel lines and filters.

Diesel fuel is the second most used fuel for internal combustionengines. It is used extensively in trucks, buses, and in heavyequipment, as well as in marine and stationary applications. Its use inpassenger cars is also growing due to the higher fuel efficiency ofcompression ignition engines over spark ignition engines.

In diesel engines, the fuel is ignited during the compression stroke bythe heat generated due to the compression of the air in the cylinder.There is a period between when the fuel is injected into the cylinderand when the compression generated heat induces the fuel to burn. Thisperiod is known as the ignition delay, and if too long, diesel knock canoccur. Other effects of long ignition delay are power loss, increasedcarbon monoxide production, and incomplete combustion, which leads toincreased hydrocarbons and particulates in the exhaust. Recently, therehas been pressure from regulatory agencies to reduce these environmentalpollutants.

An indication of how well a particular fuel will perform in acompression ignition engine is the cetane number. Poor fuels with a longignition delay have a low cetane number, while better fuels have highercetane numbers. Typical values are 40-48 for a commercial diesel fuel,and greater than 50 for a premium product. In addition to theenvironmental benefits, a high cetane fuel can decrease engine depositsand facilitate cold temperature starting.

Due to increased demand, there has been an increase in the use ofcracked materials for diesel fuel. Unfortunately, catalytic cracker,hydrocracker and coker distillates have low cetane numbers. In somecases the cetane number is below 40, which is the minimum cetane numberallowed by diesel fuel specifications. Additives known as cetaneimprovers have been developed that will raise the cetane number of adiesel fuel to acceptable levels.

Nitrate ester cetane improvers are disclosed for example in U.S. Pat.Nos. 4,705,534, 5,258,049 and 5,482,518.

Cetane improvers may destabilize diesel fuel. In a typical thermalstability test, ASTM D6468, the fuel is aged at 150° C. (302° F.) foreither 1.5 or 3.0 hours. Under these conditions, a thermally stable, lowcetane number fuel would produce very little deposits. If a commercialcetane improver such as 2-ethylhexyl nitrate was added, the fuel qualitywith respect to combustion would increase, but more deposits would beformed in the thermal stability test. In actual engines, these depositscould lead to plugged fuel lines and clogged fuel filters.

EP0947577 teaches a fuel composition that includes a cetane improver andtertiary alkyl amine thermal stabilizers. U.S. published app. No.2002/0026743 discloses the use of certain heterocyclic ring systems withlarge hydrocarbyl groups, such as polyisobutenyl succinimide, toincrease the thermal stability of a cetane improver in a fuelcomposition.

However, despite efforts to prevent the formation of insoluble materialinduced by the cetane improver, there remains a need to stabilize dieselfuels more effectively. The need is greatest for those fuels that aremore sensitive to the deleterious effects of the cetane improver.

Surprisingly, it has been found that hindered nitroxide stabilizers areespecially suited as additives which increase the thermal stability ofdiesel fuels that contain cetane improvers. The hindered nitroxidestabilizers serve to reduce the formation of insoluble material, ordeposits in the diesel fuel and thereby increase filterability andprevent plugging of fuel filters.

U.S. Pat. No. 5,711,767 discloses the use of stable nitroxide compoundsto reduce gum formation in gasoline. U.S. Pat. No. 5,460,634 teaches theuse of stable nitroxide compounds to reduce emissions produced by thecombustion of fuels.

DETAILED DISCLOSURE

The present invention pertains to a stabilized diesel fuel compositioncomprising

a) a diesel fuel with a cetane number less than or equal to 50,

b) an effective amount of at least one compound selected from the groupconsisting of the cetane improvers and

c) i) an effective stabilizing amount of at least one compound selectedfrom the group consisting of the stable nitroxide compounds or

-   -   ii) an effective synergistic stabilizing amount of at least one        compound selected from the group consisting of the stable        nitroxide compounds and at least one antioxidant compound        selected from the group consisting of the aromatic amine        antioxidants and the hindered phenolic antioxidants.

The additive combination of the stable nitroxide and the antioxidants ofcomponent c) is synergistic towards providing thermal stability.

The diesel fuel is present as the major constituent, that is present ingreater than 50 percent by weight of the total formulation.

Hydrocarbon based diesel fuels are comprised in general of mixtures ofhydrocarbons which fall within the diesel fuel boiling range, typicallyabout 160° C. to about 370° C., for example a 90% distillation pointbetween 282° C. and 338° C. (ASTM D-396 and D-975). The diesel fuel mayhave a specification that includes a minimum flash point of 38° C. Thediesel fuels are middle distillate fuels since they comprise thefractions which distill after gasoline. The diesel fuels of theinvention have a low sulfur content, for example not more than 500 ppmby weight, for instance not more than 100 ppm or not more than 60 ppm byweight sulfur. Aromatic content is in the range of 10-50% by volume, forexample about 10-35% by volume. Lower sulfur content leads to loweraromatics.

Typical cetane number values are 40-48 for a commercial diesel fuel. Thepresent diesel fuels have a cetane number of less than 50. That is, thepresent diesel fuels have an inherent cetane number of less than 50(prior to addition of any cetane improver).

The cetane improvers are for example selected from the group consistingof peroxides, for example di-t-butylperoxide, thioaldehydes, tertiaryalkyl primary amines, perketals as disclosed in U.S. Pat. No. 5,011,503,alkylether/peroxide blends as disclosed in U.S. Pat. No. 5,520,710,peracids as disclosed in EP0537931, tetrazoles and triazoles asdisclosed in U.S. Pat. No. 4,632,674, N,N-disubstituted organicnitroxides as disclosed in U.S. Pat. No. 4,398,505, organic nitrates,and mixtures thereof. The disclosures of the U.S. patents are herebyincorporated by reference.

The cetane improvers are in particular organic nitrates, for examplenitrate esters, or alkyl nitrates. Nitrate ester cetane improvers aredisclosed for example in U.S. Pat. Nos. 4,705,534, 5,258,049 and5,482,518, the disclosures of which are hereby incorporated byreference.

The nitrate esters are for example hydrocarbyl nitrates wherehydrocarbyl is a straight or branched chain alkyl of 1 to 24 carbonatoms, straight or branched chain alkyl of 2 to 24 carbon atomsinterrupted by one to three oxygen atoms, straight or branched chainalkenyl of 3 to 24 carbon atoms, cycloalkyl of 5 to 12 carbon atoms orC₁-C₄alkyl-substituted cycloalkyl of 5 to 12 carbon atoms.

Examples of hydrocarbyl are methyl, ethyl, n-propyl, isopropyl, butyl,amyl, hexyl, heptyl, octyl, isooctyl, 2-ethylhexyl, nonyl, decyl, allyl,cyclopentyl, cyclohexyl, methylcyclohexyl, cyclododecyl, 2-ethoxyethyland 2-(2-ethoxyethoxy)ethyl.

For example, the present nitrate ester is 2-ethylhexyl nitrate.

The nitroxides of this invention are for example those disclosed in U.S.Pat. Nos. 5,711,767 and 5,460,634, the disclosures of which are herebyincorporated by reference.

The nitroxide can be of several different classes. Both aromatic andaliphatic (often hindered amine) nitroxides are shown to be effective inthe present compositions. The hindered amine nitroxides are areparticular value, that is compounds with a nitroxyl moiety flanked bytwo tertiary carbon atoms. The flanking tertiary carbon atoms may befurther connected by various bridging groups to form cyclic structuressuch as for example six-membered piperidines, piperazines, five memberedpyrrolidines and the like.

The nitroxide stabilizers useful in this invention are for example ofthe formula

or are compounds that contain one or more groups of the formula

where each R is independently methyl or ethyl and T is a group requiredto complete a 5- or 6-membered ring.

Two or more nitroxide groups may be present in the same molecule bybeing linked through the T moiety as exemplified below where E is alinking group.

The stable nitroxide compounds are for example selected from the groupconsisting of bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate,4-hydroxy-1-oxyl-2,2,6,6-tetramethylpiperidine,4-ethoxy-1-oxyl-2,2,6,6-tetramethylpiperidine,4-propoxy-1-oxyl-2,2,6,6-tetramethylpiperidine,4-acetamido-1-oxyl-2,2,6,6-tetramethylpiperidine,1-oxyl-2,2,6,6-tetramethylpiperidine,1-oxyl-2,2,6,6-tetramethylpiperidin-4-one,1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl acetate,1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl 2-ethylhexanoate,1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl stearate,1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl benzoate,1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl 4-t-butyl-benzoate,bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) succinate,bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) adipate,bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) n-butylmalonate,bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) phthalate,bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) isophthalate,bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) terephthalate,bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) hexahydroterephthalate,N,N′-bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)adipamide,N-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)caprolactam,N-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)dodecylsuccinimide,2,4,6-tris-[N-butyl-N-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)]-s-triazine,4,4′-ethylenebis(1-oxyl-2,2,6,6-tetramethylpiperazin-3-one),2-oxyl-1,1,3,3-tetramethyl-2-isobenzazole,1-oxyl-2,2,5,5-tetramethylpyrrolidine,N,N-bis-(1,1,3,3-tetramethylbutyl)nitroxide, N,N-diphenylnitroxyl, amixture of mono- and dialkylatedtert-butyl/tert-octyl-N,N-diphenylnitroxyls and a mixture of mono- anddialkylated nonyl-N,N-diphenylnitroxyls.

The stable nitroxide compounds are for examplebis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate,4-hydroxy-1-oxyl-2,2,6,6-tetramethylpiperidine,4-ethoxy-1-oxyl-2,2,6,6-tetramethylpiperidine,4-propoxy-1-oxyl-2,2,6,6-tetramethylpiperidine,4-acetamido-1-oxyl-2,2,6,6-tetramethylpiperidine,1-oxyl-2,2,6,6-tetramethylpiperidine or1-oxyl-2,2,6,6-tetramethylpiperidin-4-one.

A specific embodiment is where the nitroxide compound isbis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate or4-hydroxy-1-oxyl-2,2,6,6-tetramethylpiperidine.

The aromatic amine antioxidants are for example selected from the groupconsisting of 4-(p-toluene-sulfamoyl)diphenylamine, diphenylamine,N-allyldiphenylamine, 4-isopropoxydiphenylamine,N-phenyl-1-naphthylamine, N-(4-tert-octylphenyl)-1-naphthylamine,N-phenyl-2-naphthylamine, octylated diphenylamine, for example 4,4′-di-tert-octyldiphenylamine, 4-n-butylaminophenol,4-butyrylaminophenol, 4-nonanoylaminophenol, 4-dodecanoylaminophenol,4-octadecanoylaminophenol, bis(4-methoxyphenyl)amine,2,6-di-tert-butyl-4-dimethylaminomethylphenol,2,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane,N,N,N′,N′-tetramethyl-4,4′-diaminodiphenylmethane,1,2-bis[(2-methylphenyl)amino]ethane, 1,2-bis(phenylamino)propane,(o-tolyl)biguanide, bis[4-(1′,3′-dimethylbutyl)phenyl]amine,tert-octylated N-phenyl-1-naphthylamine, a mixture of mono- anddialkylated tert-butyl/tert-octyl-diphenylamines, a mixture of mono- anddialkylated nonyidiphenylamines, a mixture of mono- and dialkylateddodecyldiphenylamines, a mixture of mono- and dialkylatedisopropyl/isohexyldiphenylamines, a mixture of mono- and dialkylatedtert-butyldiphenylamines, 2,3-dihydro-3,3-dimethyl-4H-1,4-benzothiazine,phenothiazine, a mixture of mono- and dialkylatedtert-butyl/tert-octylphenothiazines, a mixture of mono- and dialkylatedtert-octyl-phenothiazines, N-allylphenothiazine,N,N,N′,N′-tetraphenyl-1,4-diaminobut-2-ene, phenylenediamine andN,N′-di-sec-butyl-phenylenediamine.

The hindered phenolic antioxidants are for example selected from thegroup consisting of

alkylated monophenols, for example 2,6-di-tert-butyl-4-methylphenol,2,6-di-tert-butylphenol, 2-tert-butyl-4,6-dimethylphenol,2,6-di-tert-butyl-4-ethylphenol, 2,6-di-tert-butyl-4-n-butylphenol,2,6-di-tert-butyl-4-isobutylphenol, 2,6-dicyclopentyl-4-methylphenol,2-(α-methylcyclohexyl)-4,6-dimethylphenol,2,6-dioctadecyl-4-methylphenol, 2,4,6-tricyclohexylphenol,2,6-di-tert-butyl-4-methoxymethylphenol, nonylphenols which are linearor branched in the side chains, for example,2,6-di-nonyl-4-methylphenol, 2,4-dimethyl-6-(1-methylundec-1-yl)phenol,2,4-dimethyl-6-(1-methylheptadec-1-yl)phenol,2,4-dimethyl-6-(1-methyltridec-1-yl)phenol or mixtures thereof;alkylthiomethylphenols, for example2,4-dioctylthiomethyl-6-tert-butylphenol,2,4-dioctylthiomethyl-6-methylphenol,2,4-dioctylthiomethyl-6-ethylphenol or2,6-di-dodecylthiomethyl-4-nonylphenol;hindered hydroquinones, for example 2,6-di-tert-butyl-4-methoxyphenol,2,5-di-tert-butylhydroquinone, 2,5-di-tert-amylhydroquinone,2,6-diphenyl-4-octadecyloxyphenol, 2,6-di-tert-butylhydroquinone,2,5-di-tert-butyl-4-hydroxyanisole, 3,5-di-tert-butyl-4-hydroxyanisole,3,5-di-tert-butyl-4-hydroxyphenyl stearate orbis-(3,5-di-tert-butyl-4-hydroxyphenyl) adipate;tocopherols, for example α-tocopherol, β-tocopherol, γ-tocopherol,δ-tocopherol or mixtures thereof (vitamin E);hydroxylated thiodiphenyl ethers, for example 2,2′-thiobis(6-tert-butyl-4-methylphenol), 2,2′-thiobis(4-octylphenol),4,4′-thiobis(6-tert-butyl-3-methylphenol),4,4′-thiobis(6-tert-butyl-2-methylphenol),4,4′-thiobis-(3,6-di-sec-amylphenol) or4,4′-bis(2,6-dimethyl-4-hydroxyphenyl)disulfide;alkylidenebisphenols, for example 2,2′-methylenebis(6-tert-butyl-4-methylphenol),2,2′-methylenebis(6-tert-butyl-4-ethylphenol),2,2′-methylenebis[4-methyl-6-α-methylcyclohexyl)-phenol],2,2′-methylenebis(4-methyl-6-cyclohexylphenol),2,2′-methylenebis(6-nonyl-4-methylphenol),2,2′-methylenebis(4,6-di-tert-butylphenol),2,2′-ethylidenebis(4,6-di-tert-butylphenol),2,2′-ethylidenebis(6-tert-butyl-4-isobutylphenol),2,2′-methylenebis[6-α-methylbenzyl)-4-nonylphenol],2,2′-methylenebis[6-(α,α-dimethylbenzyl)-4-nonylphenol],4,4′-methylenebis(2,6-di-tert-butylphenol),4,4′-methylenebis(6-tert-butyl-2-methylphenol),1,1-bis(5-tert-butyl-4-hydroxy-2-methylphenyl)butane,2,6-bis(3-tert-butyl-5-methyl-2-hydroxybenzyl)-4-methylphenol,1,1,3-tris(5-tert-butyl-4-hydroxy-2-methylphenyl)butane,1,1-bis(5-tert-butyl-4-hydroxy-2-methyl-phenyl)-3-n-dodecylmercaptobutane,ethylene glycol bis[3,3-bis(3′-tert-butyl-4′-hydroxyphenyl)butyrate],bis(3-tert-butyl-4-hydroxy-5-methyl-phenyl)dicyclopentadiene,bis[2-(3′-tert-butyl-2′-hydroxy-5′-methylbenzyl)-6-tert-butyl-4-methylphenyl]terephthalate,1,1-bis-(3,5-dimethyl-2-hydroxyphenyl)butane,2,2-bis-(3,5-di-tert-butyl-4-hydroxyphenyl)propane,2,2-bis-(5-tert-butyl-4-hydroxy-2-methylphenyl)-4-n-dodecylmercaptobutaneor 1,1,5,5-tetra-(5-tert-butyl-4-hydroxy-2-methylphenyl)pentane;

O-, N- and S-benzyl compounds, for example 3,5,3′,5′-tetra-tert-butyl-4,4′-dihydroxydibenzyl ether,octadecyl-4-hydroxy-3,5-dimethyl benzylmercaptoacetate,tridecyl-4-hydroxy-3,5-di-tert-butylbenzylmercaptoacetate,tris(3,5-di-tert-butyl-4-hydroxybenzyl)amine,bis(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)dithioterephthalate,bis(3,5-di-tert-butyl-4-hydroxy benzyl)sulfide or isooctyl3,5-di-tert-butyl-4-hydroxybenzylmercaptoacetate;

hydroxybenzylated malonates, for example dioctadecyl2,2-bis-(3,5-di-tert-butyl-4-hydroxybenzyl)-malonate, di-octadecyl2-(3-tert-butyl-4-hydroxy-5-methylbenzyl)-malonate,didodecylmercaptoethyl-2,2-bis-(3,5-di-tert-butyl-4-hydroxybenzyl)malonateorbis[4-(1,1,3,3-tetramethylbutyl)phenyl]2,2-bis(3,5-di-tert-butyl-4-hydroxybenzyl)malonate;aromatic hydroxybenzyl compounds, for example 1,3,5-tris-(3,5-di-tert-butyl-4-hydroxy-benzyl)-2,4,6-trimethylbenzene,1,4-bis(3,5-di-tert-butyl-4-hydroxybenzyl)-2,3,5,6-tetramethylbenzene or2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)phenol;triazine compounds, for example2,4-bis(octylmercapto)-6-(3,5-di-tert-butyl-4-hydroxyanilino)-1,3,5-triazine,2-octylmercapto-4,6-bis(3,5-di-tert-butyl-4-hydroxyanilino)-1,3,5-triazine,2-octylmercapto-4,6-bis(3,5-di-tert-butyl-4-hydroxyphenoxy)-1,3,5-triazine,2,4,6-tris-(3,5-di-tert-butyl-4-hydroxyphenoxy)-1,2,3-triazine,1,3,5-tris-(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanurate,1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanurate,2,4,6-tris-(3,5-di-tert-butyl-4-hydroxyphenylethyl)-1,3,5-triazine,1,3,5-tris(3,5-di-tert-butyl-4-hydroxy-phenylpropionyl)-hexahydro-1,3,5-triazineor 1,3,5-tris(3,5-dicyclohexyl-4-hydroxybenzyl)isocyanurate;benzylphosphonates, for example dimethyl2,5-di-tert-butyl-4-hydroxybenzylphosphonate,diethyl-3,5-di-tert-butyl-4-hydroxybenzylphosphonate, dioctadecyl3,5-di-tert-butyl-4-hydroxybenzylphosphonate, dioctadecyl5-tert-butyl-4-hydroxy-3-methylbenzylphosphonate or the calcium salt ofthe monoethyl ester of 3,5-di-tert-butyl-4-hydroxybenzylphosphonic acid;acylaminophenols, for example 4-hydroxylauranilide,4-hydroxystearanilide or octylN-(3,5-di-tert-butyl-4-hydroxyphenyl)carbamate;esters of β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid withmono- or polyhydric alcohols, e.g. with methanol, ethanol, butanol,n-octanol, isooctanol (a mixture of octanols), octadecanol,1,6-hexanediol, 1,9-nonanediol, ethylene glycol, 1,2-propanediol,neopentyl glycol, thiodiethylene glycol, diethylene glycol, triethyleneglycol, pentaerythritol, tris(hydroxyethyl) isocyanurate,N,N′-bis(hydroxyethyl)oxamide, 3-thiaundecanol, 3-thiapentadecanol,trimethylhexanediol, trimethylolpropane or4-hydroxymethyl-1-phospha-2,6,7-trioxabicyclo[2.2.2]octane;esters of β-(5-tert-butyl-4-hydroxy-3-methylphenyl) propionic acid withmono- or polyhydric alcohols, e.g. with methanol, ethanol, n-octanol,isooctanol (a mixture of octanols), octadecanol, 1,6-hexanediol,1,9-nonanediol, ethylene glycol, 1,2-propanediol, neopentyl glycol,thiodiethylene glycol, diethylene glycol, triethylene glycol,pentaerythritol, tris(hydroxyethyl) isocyanurate,N,N′-bis(hydroxyethyl)oxamide, 3-thiaundecanol, 3-thiapentadecanol,trimethylhexanediol, trimethylolpropane or4-hydroxymethyl-1-phospha-2,6,7-trioxabicyclo[2.2.2]octane;esters of β-(3,5-dicyclohexyl-4-hydroxyphenyl) propionic acid with mono-or polyhydric alcohols, e.g. with methanol, ethanol, octanol, isooctanol(a mixture of octanols), octadecanol, 1,6-hexanediol, 1,9-nonanediol,ethylene glycol, 1,2-propanediol, neopentyl glycol, thiodiethyleneglycol, diethylene glycol, triethylene glycol, pentaerythritol,tris(hydroxyethyl)isocyanurate, N,N′-bis(hydroxyethyl)ox-amide,3-thiaundecanol, 3-thiapentadecanol, trimethylhexanediol,trimethylolpropane or4-hydroxymethyl-1-phospha-2,6,7-trioxabicyclo[2.2.2]octane; esters of3,5-di-tert-butyl-4-hydroxyphenyl acetic acid with mono- or polyhydricalcohols, e.g. with methanol, ethanol, octanol, isooctanol (a mixture ofoctanols), octadecanol, 1,6-hexanediol, 1,9-nonanediol, ethylene glycol,1,2-propanediol, neopentyl glycol, thiodiethylene glycol, diethyleneglycol, triethylene glycol, pentaerythritol,tris(hydroxyethyl)isocyanurate, N,N′-bis(hydroxyethyl)oxamide,3-thiaundecanol, 3-thiapentadecanol, trimethylhexanediol,trimethylolpropane or4-hydroxymethyl-1-phospha-2,6,7-trioxabicyclo[2.2.2]octane;

and

amides of β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid e.g.N,N′-bis(3,5-di-tert-butyl-4-hydroxyphenylpropionyl)hexamethylenediamide,N,N′-bis(3,5-di-tert-butyl-4-hydroxyphenylpropionyl)trimethylenediamide,N,N′-bis(3,5-di-tert-butyl-4-hydroxyphenylpropionyl)hydrazide orN,N′-bis[2-(3-[3,5-di-tert-butyl-4-hydroxyphenyl]propionyloxy)ethyl]oxamide(Naugard® XL-1 supplied by Uniroyal).

For example, the antioxidant compound is diphenylamine, a mixture ofmono- and dialkylated tert-butyl/tert-octyl-diphenylamines, a mixture ofmono- and dialkylated nonyldiphenylamines, phenylenediamine orN,N′-di-sec-butyl-phenylenediamine.

The effective stabilizing amount of component c) is from about 0.05 ppmto about 10,000 ppm, by weight, based on the weight of the fuelcomposition. For example component c) is present from about 0.1 ppm toabout 1000 ppm, from about 0.2 ppm to about 100 ppm, or from about 0.5ppm to about 25 ppm. For example, component c) is present from about0.05 ppm to about 1000 ppm, from about 0.05 ppm to about 100 ppm, orfrom about 0.05 ppm to about 25 ppm, based on the entire fuelformulation. For instance, component c) is present from about 0.1 ppm toabout 10,000 ppm, from about 0.2 ppm to about 10,000 ppm, or from about0.5 ppm to about 10,000 ppm, based on the weight of the entire fuelformulation.

The ratio of the stable nitroxides to the antioxidants is for examplefrom about 1:99 to about 95:5 parts by weight. For example, the ratio ofthe stable nitroxides to the antioxidants by weight is from about 1:10to about 10:1, from about 1:5 to about 5:1, from about 1:3 to about 3:1,or about 1:1 parts by weight. The ratio of the stable nitroxides to theantioxidants is for example about 1:4 parts by weight.

The present stabilized compositions exhibit excellent filterability.Accordingly, provided is a process for improving the filterability andimproving the cetane number of a diesel fuel, which process comprises

adding to a diesel fuel with a cetane number less than or equal to 50,

b) an effective amount of at least one compound selected from the groupconsisting of the cetane improvers and

c) i) an effective stabilizing amount of at least one compound selectedfrom the group consisting of the stable nitroxide compounds or

-   -   ii) an effective synergistic stabilizing amount of at least one        compound selected from the group consisting of the stable        nitroxide compounds and at least one antioxidant compound        selected from the group consisting of the aromatic amine        antioxidants and the hindered phenolic antioxidants.

Other traditional additives may also be present in the compositions andprocesses of this invention. Other additives include for exampledispersants, for example hydrocarbyl-substituted succinimides orsuccinamides and hydrocarbylpolyamines; metallic based combustionimprovers such as ferocene, corrosion inhibitors, other antioxidantssuch as amine-formaldehyde products, anti-foams, deodorants, anti-wearagents, flow improvers, wax antisettling additives or other operabilityimprovers, cloud point depressants, friction modifiers, solubilizers,anti-rust agents, detergents lubricants, other heat stabilizers, and thelike. Other additives may be present from about 5 ppm to about 500 ppmby weight based on the weight of the entire formulation.

The invention is illustrated by the following non-limiting Example.Unless otherwise noted, parts and percentages are by weight.

EXAMPLE 1 Diesel Fuel Filterability

Filterability is determined according to ASTM test method D6468. Adiesel fuel sample is heated under air to 150° C. for either 90 or 180minutes. The fuel is then filtered, and the amount of deposits on thefilter paper is measured by reflectivity. The more deposits trapped onthe filter, the lower the reflectivity of the filter pad. Too manydeposits will clog filters in actual use.

The table below demonstrates results with two different low sulfurdiesel fuels. Percent reflectance is measured on samples heated to 150°C. for 90 minutes. Levels are ppm based on the fuel formulation.

Cmpd Cmpd Cmpd Blend Percent Formulation 2-EHN 1 2 3 1 Reflectance A 0 —— — — 94 B 1500 — — — — 69 D 1500 1.4 — — — 74 E 1500 10.4 — — — 78 F 0— — — — 95 G 1500 — — — — 73 H 1500 — 1.0 — — 74 I 1500 — 10.0 — — 78 J1500 — — 1.0 — 80 K 1500 — — 10.0 — 84 L 1500 — — — 1.0 79 M 1500 — — —10.0 84

2-EHN is 2-ethylhexyl nitrate cetane improver.

Cmpd 1 is bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate.

Cmpd 2 is 1-oxyl-4-hydroxy-2,2,6,6-tetramethylpiperidine.

Cmpd 3 is 1-oxyl-4-n-propoxy-2,2,6,6-tetramethylpiperidine.

Blend 1 is 14% Cmpd 1, 56% by weight mixture of mono- and dialkylatedtert-butyl/tert-octyl-diphenylamines, 30% inert aromatic solvent (byweight).

Formulations A-E are with Diesel Fuel 1. Formulations F-M are withDiesel Fuel 2. The two fuels are within ASTM D975 specifications (dieselfuel specifications) according to the present invention.

It is seen that the cetane improver significantly reduces thefilterability of the diesel fuel. Even at a level of 1 ppm of addedstable nitroxide compound, there is a marked decrease in precipitate asindicated by a measurable increase in filter pad reflectance. Thus, withthe use of the nitroxide alone or in combination with antioxidants,there will be a reduced tendency for diesel fuel to form insolublematerial that could plug fuel filters and lines.

1. A stabilized diesel fuel composition comprising a) a diesel fuel witha cetane number less than or equal to 50, b) 2-ethylhexyl nitrate cetaneimprover and c) i) at least one stable nitroxide compound selected frombis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate and4-hydroxy-1-oxyl-2,2,6,6-tetramethylpiperidine or ii) at least onestable nitroxide compound selected frombis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate and4-hydroxy-1-oxyl-2,2,6,6-tetramethylpiperidine and at least oneantioxidant compound selected from the group consisting of aromaticamine antioxidants and hindered phenolic antioxidants, where componentc) is present from about 0.05 ppm to about 10,000 ppm, by weight, basedon the weight of the entire formulation.
 2. A composition according toclaim 1 in which component c) is present from about 0.1 ppm to about1000 ppm, by weight, based on the weight of the entire formulation.
 3. Acomposition according to claim 1 in which component c) is present fromabout 0.2 ppm to about 100 ppm, by weight, based on the weight of theentire formulation.
 4. A composition according to claim 1 in whichcomponent c) is present from about 0.5 ppm to about 25 ppm, by weight,based on the weight of the entire formulation.
 5. A compositionaccording to claim 1 comprising at least one compound selected from thegroup consisting of the stable nitroxide compounds and at least oneantioxidant compound selected from the group consisting of the aromaticamine antioxidants and the hindered phenolic antioxidants.
 6. Acomposition according to claim 5 in which the ratio of the stablenitroxide compounds to the antioxidant compounds is from about 1:99 toabout 95:5 parts by weight.
 7. A composition according to claim 5 inwhich the ratio of the stable nitroxide compounds to the antioxidantcompounds is from about 1:10 to about 10:1 parts by weight.
 8. Acomposition according to claim 5 in which the ratio of the stablenitroxide compounds to the antioxidant compounds is from about 1:5 toabout 5:1 parts by weight.
 9. A composition according to claim 5 inwhich the ratio of the stable nitroxide compounds to the antioxidantcompounds is from about 1:3 to about 3:1 parts by weight.
 10. A processfor improving the filterability and improving the cetane number of adiesel fuel, which process comprises adding to a diesel fuel with acetane number less than or equal to 50, b) 2-ethylhexyl nitrate cetaneimprover and c) i) at least one stable nitroxide compound selected frombis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate and4-hydroxy-1-oxyl-2,2,6,6-tetramethylpiperidine or ii) at least onestable nitroxide compound selected frombis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate and4-hydroxy-1-oxyl-2,2,6,6-tetramethylpiperidine and at least oneantioxidant compound selected from the group consisting of aromaticamine antioxidants and hindered phenolic antioxidants, where componentc) is added from about 0.05 ppm to about 10,000 ppm, by weight, based onthe weight of the entire formulation.